Recent evidence obtained in our laboratory suggests that a 22,000 molecular weight protein of the cardiac sarcoplasmic reticulum (SR) mediates part of the mechanical response of the mammalian myocardium to inotropic agents such as epinephrine. Abbreviation of systole or increased rate of relaxation after epinephrine administration may be accounted for by an increased transport of calcium into the SR. Our previous evidence has indicated that cyclic AMP, whose formation is increased by catecholamines and other agents, activates the enzyme protein kinase. We have demonstrated (1) that cyclic AMP-dependent protein kinase catalyzes the phosphorylation of a 22,000 dalton protein and (2) that this phosphorylation is closely correlated with an increase in calcium pump activity of the cardiac SR. In the present project, the 22,000 dalton protein will be purified and characterized. We will establish its molecular weight by methods other than SDS-gel electrophoresis, determine its amino acid composition, number of phosphorylation sites, ability to bind calcium, and various other properties. BIBLIOGRAPHIC REFERENCES: Tada, M., M.A. Kirchberger, and A.M. Katz. Phosphorylation of a 22,000 dalton component of the cardiac sarcoplasmic reticulum by adenosine 3':5'-monophosphate-dependent protein kinase. J. Biol. Chem. 250:2640-2647, 1975; Katz, A.M., M. Tada, and M.A. Kirchberger. Control of calcium transport in the myocardium by the cyclic AMP-protein kinase system. Adv. Cyclic Nuc. Res. 5: 453-472, 1975.